1. Field of the Invention
The present invention relates to a carriage structure of an NC lathe.
2. Description of the Prior Art
In a conventional NC lathe for machining a work W to form a shape as shown in FIGS. 31 to 33, an initial set-up step including an operation for chucking the work W and a subsequent operation for centering the work W by a tailstock and bracing means. A first machining step is thereafter performed and includes a turning operation for an outer surface of the work W to form a stepped portion 1 having surfaces 1a, 1b and 1c, another turning operation to form an inner surface 2 and an operation for threading the surface 1a to form a thread 3.
A second machining step is subsequently performed to form a flange portion 4 and its end portion 5. Before performing the second machining step, the work W machined through the first machining step is removed from a chuck of the NC lathe and is thereafter again mounted on the chuck at an inverted position. The work W thus mounted on the chuck is centered for the second machining step.
The work W machined through the second machining step is transferred to a vertical machining center at which the work W is again centered for a third machining step to form a key recess 6 and to machine first fl at surfaces 7 and second flat surfaces 8 through indexing operations. The work W machined through the third machining step is thereafter transferred to a horizontal machining center at which the work is again centered for a fourth machining step to finally form holes 9 on the end portion 5 through a drill-tapping operation.
The above conventional machining steps, however, consumes much time for transferring the work W for each subsequent machining step and also consumes much time for centering the work W at each subsequent machining step. Further, this may degrade the quality of the work W and cause problems in introduction of automatic operation.